1. Field of the Invention
The present invention generally relates to methods for predicting reservoir properties. Particularly, the present invention relates to predicting reservoir properties using well data and seismic data. More particularly, the present invention relates to predicting reservoir properties using well data from a horizontal well.
2. Description of the Related Art
Seismic data properly acquired and processed may provide a wealth of information to an explorationist, one of the individuals within an oil company whose job it is to locate potential drilling sites. For example, a seismic profile gives the explorationist a broad view of the subsurface structure of the rock layers and often reveals important features associated with the entrapment and storage of hydrocarbons such as faults, folds, anticlines, unconformities, and sub-surface salt domes and reefs, among many others. This wealth of information increases the probability that a selected site will result in a productive well.
Seismic data is generally acquired by performing a seismic survey. A seismic survey maps the subsurface of the earth by sending sound energy down into the ground and recording the “echoes” that return from the rock layers below. The source of the down-going sound energy might come from explosions, seismic vibrators on land, or air guns in marine environments. During a seismic survey, the energy source is moved to multiple preplanned locations on the surface of the earth above the geologic structure of interest. Each time the source is activated, it generates a seismic signal that travels downward through the earth, is reflected, and, upon its return, is recorded at a great many locations on the surface. Multiple energy activation/recording combinations are then combined to create a near continuous profile of the subsurface that can extend for many miles. In a two-dimensional (2-D) seismic survey, the recording locations are generally laid out along a single straight line, whereas in a three-dimensional (3-D) survey the recording locations are distributed across the surface in a grid pattern. In simplest terms, a 2-D seismic line can be thought of as giving a cross sectional picture (vertical slice) of the earth layers as they exist directly beneath the recording locations. A 3-D survey produces a data “cube” or volume that is, at least conceptually, a 3-D picture of the subsurface that lies beneath the survey area.
After the survey is acquired, the data from the survey is processed to remove noise or other undesired information. During the computer processing of seismic data, estimates of subsurface velocity are routinely generated and near surface inhomogeneities are detected and displayed. In some cases, seismic data can be used to directly estimate rock porosity, water saturation, and hydrocarbon content. Less obviously, seismic waveform attributes such as phase, peak amplitude, peak-to-trough ratio, and a host of others, can often be empirically correlated with known hydrocarbon occurrences and that correlation applied to seismic data collected over new exploration targets. In brief, seismic data provides some of the best subsurface structural and stratigraphic information that is available, short of drilling a well.
To improve the usefulness of seismic data, a variety of techniques exist for enhancing the seismic information with other data. However, one problem in using seismic attributes is that their relation to actual rock properties is not obvious. There are unknown local factors that may affect the data in unexpected ways, and it is risky to predict functional relationships among seismic attributes and reservoir properties based on a simplified theoretical analysis with no familiarity of what “works” in a certain region. This problem is exacerbated by the fact that the wellbore data is traditionally derived from vertical or deviated wells. Because geological features are generally oriented parallel to the surface of the earth, a vertical or deviated well will only intersect a narrow region of the geological feature. As a result, the well will only provide data for a narrow region of the seismic attribute. Thus, many costly wells must be drilled to obtain the amount of data needed to obtain a sufficient level of region familiarity.
There is a need, therefore, for methods for predicting reservoir properties. Further, there is a need for methods for building knowledge of the area and for estimating reservoir properties with a minimum number of wells. There is also a need for methods for predicting reservoir properties using well production data.